The precise regulation of gene transcription in the developing airway epithelium is critical to the differentiation of epithelial cell lineages required for postnatal respiration as well as injury repair. However, little is known about the transcriptional pathways involved in regulating lung epithelial specific gene expression. The forkhead/winged-helix (also known as Fox) family of transcription factors is known to play an important role in the regulation of gene expression and cell differentiation. We have cloned a new subfamily of Fox transcription factors, Foxp1 and Foxp2, which are expressed at high levels in the embryonic and adult airway epithelium. Expression of Foxp1 is found at high levels in the distal airway epithelium and at lower levels in the proximal airway epithelium. Notably, Foxp2 is the first Fox gene described expressed exclusively in the distal airway epithelium in the lung. Preliminary analysis shows that Foxp1 and -2 repress the lung specific promoters for the SP-C and CC10 genes and that this repression activity is localized to a unique and homologous domain in the amino-terminus of both proteins that contains several putative protein-protein interaction motifs. These results lead us to hypothesize that Foxp1 and -2 regulate lung epithelial gene transcription via unique mechanisms involving transcriptional repression, possibly modulated through interaction with co-regulatory molecules. To test this hypothesis we propose to: 1) determine the precise gene and protein expression patterns of Foxp1 and -2 during development which should provide important clues as to potential down-stream transcriptional targets of these genes as well as interacting co-regulatory molecules, 2) precisely define the structural domains within Foxp1 and -2 that are important for transcriptional activity, 3) characterize the Foxp1/2-CtBP-1 interaction and its affect on the transcriptional activity of Foxp1 and -2, and 4) determine the role of Foxp1 and -2 in the development of airway epithelium through the analysis of Foxp1 and -2 deficient mice. These studies will greatly enhance our understanding of the specific transcriptional pathways that regulate lung epithelial development and differentiation as well as the mechanisms behind the pathogenesis of lung diseases, which occur due to aberrant epithelial differentiation and function.